Communication devices such as User Equipments (UEs) are enabled to communicate wirelessly in a cellular communications network or wireless communication system, sometimes also referred to as a cellular radio system or cellular networks. The communication may be performed e.g. between two UEs, between a UE and a regular telephone and/or between a UE and a server via a Radio Access Network (RAN) and possibly one or more core networks, comprised within the cellular communications network.
UEs may further be referred to as wireless terminals, mobile terminals and/or mobile stations, mobile telephones, cellular telephones, laptops, tablet computers or surf plates with wireless capability, just to mention some further examples. The UEs in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the RAN, with another entity, such as another wireless terminal or a server. The following commonly terminologies are used in the embodiments and are elaborated below:
The non-limiting term radio network node is more commonly used and it refers to any type of network node serving UE and/or connected to other network node or network element or any radio node from where UE receives signal. Examples of radio network nodes are Node B, base station (BS), multi-standard radio (MSR) radio node such as MSR BS, eNode B, network controller, radio network controller (RNC), base station controller, relay, donor node controlling relay, base transceiver station (BTS), access point (AP), transmission points, transmission nodes, RRU, RRH, nodes in distributed antenna system (DAS) etc.
A more general term “network node” is used and it can correspond to any type of radio network node or any network node, which communicates with at least a radio network node. Examples of network node are any radio network node stated above, core network node (e.g. MSC, MME etc), O&M, OSS, SON, positioning node (e.g. E-SMLC), MDT etc.
The cellular communications network covers a geographical area which is divided into cell areas, wherein each cell area being served by a network node. A cell is the geographical area where radio coverage is provided by the network node.
The network node may further control several transmission points, e.g. having Radio Units (RRUs). A cell can thus comprise one or more network nodes each controlling one or more transmission/reception points. A transmission point, also referred to as a transmission/reception point, is an entity that transmits and/or receives radio signals. The entity has a position in space, e.g. an antenna. A network node is an entity that controls one or more transmission points. The network node may e.g. be a base station such as a Radio Base Station (RBS), eNB, eNodeB, NodeB, B node, or BTS (Base Transceiver Station), depending on the technology and terminology used. The base stations may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size.
Further, each network node may support one or several communication technologies. The network nodes communicate over the air interface operating on radio frequencies with the UEs within range of the network node. In the context of this disclosure, the expression Downlink (DL) is used for the transmission path from the base station to the mobile station. The expression Uplink (UL) is used for the transmission path in the opposite direction i.e. from the UE to the base station.
In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), base stations, which may be referred to as eNodeBs or even eNBs, may be directly connected to one or more core networks. In LTE the cellular communication network is also referred to as Evolved Universal Terrestrial Radio Access Network (E-UTRAN).
An E-UTRAN cell is defined by certain signals which are broadcasted from the eNB. These signals contain information about the cell which can be used by UEs in order to connect to the network through the cell. The signals comprise reference and synchronization signals which the UE uses to find frame timing and physical cell identification as well as system information which comprises parameters relevant for the whole cell.
A UE needing to connect to the network must thus first detect a suitable cell, as defined in 3GPP TS 36.304 v11.5.0. The UE can be in either idle state, which is also referred to as IDLE or RRC_IDLE, or in connected state, which state is also referred to as CONNECTED or RRC_CONNECTED. When the UE is in RRC_IDLE, it monitors a paging channel, which paging channel is part of a Paging Control Channel (PCCH) at a logical level, a Paging Channel (PCH) on a transport channel level and a Physical Downlink Shared Channel (PDSCH) on a physical channel level. While doing so the UE typically also performs a number of radio measurements which it uses to evaluate the best cell, such as Reference Signal Receive Power (RSRP), Reference Symbol Received Quality (RSRQ) or Received Signal Strength Indicator (RSSI). This is performed by measuring on received reference signals and/or parts of a spectrum which comprises reference signals sent by cells. This may also be referred to as “listening” for a suitable cell.
A suitable cell is commonly a cell which has RSRQ or RSRP above a certain level. The cell with the highest RSRP or RSRQ may be referred to as the best cell or the best suitable cell. Listening for a suitable cell may comprise searching for reference signals transmitted from one or more network nodes in an OFDM subframe. When the best suitable cell is found the UE performs random access, according to a system information for the cell. This is done in order to transmit a Radio Resource Control (RRC) connection setup request to the network node. Assuming the random access procedure succeeds and the network node receives the request, the network node will either answer with an RRC connection setup message, which acknowledges the UEs request and tells it to move into RRC connected state, or an RRC connection reject, which tells the UE that it may not connect to the cell. In RRC connected state the parameters necessary for communication between the network node and the UE are known to both entities and a data transfer between the two entities is enabled.
When the UE is in RRC_CONNECTED state the UE continues to measure RSRP, as well as an input to connected mode mobility decisions, such as e.g. performing a handover from one cell to another. These measurements are typically performed in the full bandwidth, which may also be referred to as the full spectrum, of the subframe.
RSRP is a measurement of the signal strength of an LTE cell which helps the UE to rank the different cells according to their signal strength as input for handover and cell reselection decisions. The RSRP is an average of a power of all resource elements which carry Cell-specific Reference Signals (CRS) over the entire bandwidth. It is therefore only measured in OFDM symbols carrying CRS.
In a mobile radio communication systems air interface resources are allocated to UEs on a short timescale. This allocation task may be performed by a scheduler in the network node. The scheduler tries to assign resources to a UE to fulfill Quality of Service (QoS) requirements. The QoS requirements are in LTE expressed per radio bearer, represented by QoS Class Identifier (QCI) and Allocation and Retention Priority (ARP). Whenever the scheduler is congested, i.e. when there are no available resources for scheduling UEs, the scheduler assigns resources such that the QoS requirements are fulfilled in the order indicated by the priority of the QoS. In LTE, these resources are typically CCEs of the PDCCH and Physical Resource Blocks (PRBs) of PDSCH/PUSCH. In LTE 3GPP Rel-11 a new downlink control channel, EPDCCH, is introduced. Similar to PDCCH, EPDCCH may be used to transmit Downlink Control Indications (DCI) to UEs connected to the cell. A difference between PDCCH and EPDCCH is that while PDCCH is transmitted in a control region, separate from the region used for PDSCH, the EPDCCH is multiplexed with PDSCH. There are however some problems related to this way of prioritizing with respect to QoS requirements.
Firstly, some radio bearers may not have any QoS requirements at all, these may e.g. be referred to as best-effort or non-Guaranteed Bit Rate (non-GBR) bearers. This means that scheduling will not consider these radio bearers in congested scenarios. Hence, there is a risk that this class of radio bearers is starved out since only radio bearers with specified QoS requirements are scheduled.
Secondly, if too many radio bearers with QoS requirements are admitted the scheduler will at some point fail to provide resources to all of these radio bearers. Users may have been admitted at a point in time when radio conditions and mobility were favorable in the sense that QoS could be provided. Hence, due to increasing mobility and worsened radio conditions the resources may at a later point in time not be enough to provide QoS for the admitted radio bearers.